| 高镍铜镍矿床的特征、形成机制与勘查展望 |
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| 引用本文： | 毛亚晶,秦克章,唐冬梅.高镍铜镍矿床的特征、形成机制与勘查展望[J].岩石学报,2018,34(8):2410-2424. |
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| 作者姓名： | 毛亚晶 秦克章 唐冬梅 |
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| 作者单位： | 中国科学院矿产资源研究重点实验室中国科学院地质与地球物理研究所;中国科学院地球科学研究院;中国科学院大学 |
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| 基金项目： | 本文受国家自然科学基金项目（41502095、41872094）资助. |
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| 摘 要： | 岩浆铜镍矿床100%硫化物中的Ni含量与赋矿岩石和成矿过程紧密相关,记录岩浆成分、分异程度与硫化物演化过程。硫化物异常高镍(高镍硫化物)往往被认为与科马提质岩浆或者后期热液作用密切相关。近年研究结合勘查证实,赋含高镍硫化物的矿床(高镍铜镍矿床)不仅限于科马提岩,还与苦橄质、玄武质岩浆有关,另外,热液富集作用并不是必要因素。本文总结了世界上高镍铜镍矿床的基本特征和形成机制,分析提出了不同机制的判别标志,并展望了其勘查前景。详细对比高镍铜镍矿床的产出环境、赋矿岩相、矿石特征、矿物组合等特征,该类矿床往往产于大陆裂谷和造山带环境,与基性程度较高的岩浆有关,以橄榄岩赋矿为主,含镍硫化物组合主要为镍黄铁矿-磁黄铁矿-黄铜矿组合,少数为针镍矿-镍黄铁矿-黄铁矿组合。科马提岩相关矿床可将Ni含量大于16%的硫化物定义为高镍硫化物,苦橄质-玄武质岩浆相关矿床的硫化物可分为高镍硫化物(Ni10%)、中镍硫化物(5%～10%)和富铜硫化物(Ni5%,CuNi)。原生高镍硫化物可由富镍岩浆熔离、硫化物从橄榄石中吸取Ni、硫化物结晶分异、硫化物与硫不饱和岩浆反应等机制形成。苦橄质-玄武质岩浆相关的矿床,硫化物与橄榄石的Fe-Ni交换反应是高镍硫化物形成的重要机制。辉石岩源区地幔部分熔融形成富镍岩浆是否为高镍硫化物形成的必要条件尚存争议。不同机制形成的高镍硫化物具有迥异的岩石-矿物组合和地化特征。硫化物矿物组合、橄榄石成分(Fo值、Ni含量、Fo值-Ni含量的相关性)、伴生元素(铜、铂族元素)丰度-配分模式等特征可作为区分不同高镍硫化物形成机制的有效指标。我国新疆黄山南、坡一和青海夏日哈木矿床(部分浸染状矿化橄榄岩)以赋含高镍硫化物为特征,新疆喀拉通克矿床的硫化物则以富铜为特征,中国其余矿床的硫化物均属中镍硫化物。目前研究指示中国的高镍铜镍矿床与母岩浆相对富镍、硫化物与橄榄石Fe-Ni交换作用密切相关,后者可使硫化物Ni含量提升3%～5%。在铜镍矿床勘查方面,稀疏-中等浸染状高镍硫化物矿石即可达到工业品位,稠密浸染状-块状高镍硫化物矿石可达到很高的Ni品位(10%),是高品位镍矿勘查的一个重要方向。造山带环境富水、相对高氧逸度(可高达QFM+1)的岩浆可能是形成高镍硫化物的有利条件,该环境橄榄石Fo值较高(87mol%)的岩体有利于形成高镍硫化物。
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| 关 键 词： | 岩浆铜镍矿床 高镍硫化物 黄山南 坡一 夏日哈木 造山带铜镍矿勘查 |
| 收稿时间： | 2018/2/1 0:00:00 |
| 修稿时间： | 2018/3/23 0:00:00 |
Characteristics, genetic mechanism, and exploration perspective of Ni-rich sulfide in magmatic Ni-Cu systems |
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| MAO YaJing,QIN KeZhang and TANG DongMei.Characteristics, genetic mechanism, and exploration perspective of Ni-rich sulfide in magmatic Ni-Cu systems[J].Acta Petrologica Sinica,2018,34(8):2410-2424. |
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| Authors: | MAO YaJing QIN KeZhang and TANG DongMei |
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| Institution: | Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China,Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China;University of Chinese Academy of Sciences, Beijing 100049, China and Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China |
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| Abstract: | Nickel content in sulfide (Ni tenor) is an important parameter in magmatic Ni-Cu deposit. It records Ni content in magma, the degrees of magma evolution and sulfide fractionation. Generally, high-Ni tenor sulfides are believed to be associated with komatiitic magma or alteration processes. However, it is shown that some of the high-Ni tenor sulfides could also be generated by basaltic, picritic magmas without secondary alteration process. This study summarized the characteristics and genetic mechanism of the Ni-Cu deposits having high-Ni tenor sulfides, proposed the discernment sign for different mechanisms, discussed its exploration prospect. The high Ni tenor deposits commonly occur in continental rift and orogenic belts and hosted by olivine-rich rocks, forming by less evolved magmas which are relatively enriched in Ni. The primary Ni-bearing mineral is dominantly by pentlandite, but some komatiitic related deposits are dominated by millerite. According to the Ni tenor in sulfide, the komatiitic related sulfides having higher than 16% Ni could be defined as high-Ni tenor, whereas the non-komatiitic related sulfides could be defined as high Ni tenor (Ni>10%), medium Ni tenor (5%~10%), and low Ni tenor (Ni<5%, Cu>Ni). The primary high Ni sulfide can be formed by segregation from Ni-rich magma, the absorption of Ni from olivine, the sulfide fractional crystallization, and the reaction of sulfide with sulfur-unsaturated magma. For picritic and basaltic magmas (relatively Ni-rich), Fe-Ni exchange between sulfide and olivine is an important mechanism. Whether the partial melting of the pyroxene mantle source is a necessary condition for the formation of high-Ni tenor sulfides remains debatable. The high-Ni sulfides formed by different mechanisms have diverse rock-mineral assemblages and geochemical characteristics, i.e. sulfide mineral assemblages, olivine components (Fo values, Ni contents, correlations between Fo values versus Ni content), chalcophile element (copper, platinum group elements) abundance in sulfide. Thus, these features are valid indicators of the different high-Ni sulfide formation mechanisms. In China, the sulfides in the Huangshannan, Poyi, and Xiarihamu deposits are characterized by high-Ni tenor, whereas those in the Kalatongke deposit are featured by low-Ni and high-Cu tenor. Recent research indicates that Ni-rich sulfide hosting deposits in China were formed by relatively Ni-rich parent magma and Fe-Ni exchange between sulfide and olivine, the latter factor results in 3%~5% Ni tenor increase in the sulfide. For exploration in high-Ni sulfide bearing intrusions, industrial Ni grades could be achieved for sparse disseminated ores, whereas very high Ni grade could be achieved for densely disseminated ores. Therefore, these intrusions are capable of exploring high-grade Ni ores. In orogenic belts, magmas with relatively high oxygen fugacity (up to QFM+1) and water may provide favorable conditions for the formation of high-Ni sulfides. In such setting, intrusions with olivine high Fo values (>87mol%) may host high Ni sulfides. |
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| Keywords: | Magmatic sulfide deposit High Ni tenor sulfide Huangshannan Poyi Xiarihamu Orogenic Ni-Cu deposit exploration |
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